Swarm Keeper is a Dungeon Keeper inspired modification for Alien Swarm. It offers the following features: Build a dungeon for your creatures (aliens), imps which perform tasks for you (like digging blocks away, collecting gold), a portal through which creatures enter your dungeon, different room types (treasure, lair, hatchery and training), a dungeon heart, which must be protected from enemies and invading marines as enemies.
This mod should be considered as an experiment to bring a Dungeon Keeper like game to the Source Engine.

Swarm Keeper is a Dungeon Keeper inspired modification for Alien Swarm. The current release offers the following features:

Build a dungeon for your creatures

Order your imps to perform tasks like digging and collect gold

Four different rooms: treasure, lair, hatchery and training

Several basic spells

A random level generator, supporting up to 170x170 tiles

Waves of invading marines as enemies

This release is still more of a demo (i.e. only basic mechanics like imps, digging, creatures routines, basic room types, gold collection, etc) and the actually direction of the mod is still pretty much open.

Some thought on that:
You can make Hive-Mind simulator, swarm-controler infesting different parts of colony. Like, you start with your "brain" and few drones somewhere in maintenance shafts, you "dig" through pipes, intersections, capture living(or not so) colonists for making creatures(or food) from them. "Building" biomass barricades, resource-transporting pipelines, maybe repurposing some station equipment to create some unique monsters or gain unique options.
I mean that you can make something new, basing on DK experience and feel, instead of porting DK on source and replacing imps with swarm and knights with marines. Just thinking.

I completely agree, I still play Dungeon Keeper 2, and as the Swarm Keeper name suggests, it should heavily based on Alien Swarm content (creatures, rooms, etc) but with the DK2 gameplay as B.R.V stated.